Three dimensional structure of the seventh transmembrane helical domain ofthe G-protein receptor, rhodopsin

PURPOSE: The three dimensional structure of a peptide comprising the sequen ce of the seventh transmembrane segment of the G-protein coupled receptor, rhodopsin, was determined in solution. METHODS: The sequence of the seventh transmembrane segment of rhodopsin, wh ich contains the NPxxY sequence that is highly conserved among G-protein co upled receptors and lys296 that forms the Schiff base with the retinal, was synthesized by solid phase peptide synthesis. The three dimensional struct ure was determined in solution by high-resolution nuclear magnetic resonanc e (NMR). RESULTS: The structure revealed a helix-break-helix motif for this sequence . Two families of structures were observed which differed in the angle betw een the two helical segments. The sequence of this transmembrane segment ov erlapped significantly the sequence of a peptide from the carboxyl terminal of rhodopsin, the structure of which was solved previously. The redundant sequence formed a helix in both peptides. It was therefore possible to supe rimpose the redundant sequence of both peptides and construct a structure f or rhodopsin encompassing residues 291-348. CONCLUSIONS: This structure reveals locations of the lys296 and the acylati on sites of rhodopsin that are consistent with the known biochemistry of th is receptor. This segmentation approach to membrane protein structure provi des important structural information in the absence of an X-ray crystal str ucture of rhodopsin. The approach is expected to be useful for other G-prot ein coupled receptors.